A typical full width printer uses one or more printheads. The printheads are arranged in one or more arrays to enable a solid line at a predetermined resolution to be formed across the width of a planar member. The planar member can be a sheet of media in inkjet image printers or a platen in three-dimensional (3D) object printers. Each printhead typically contains an array of individual nozzles for ejecting drops of ink or material across an open gap to the planar member to form an image or layer on the member. In each printhead, individual piezoelectric, thermal, or acoustic actuators generate mechanical forces that expel ink or material through an orifice or nozzle in response to an electrical voltage signal, sometimes called a firing signal. The amplitude, frequency, or duration of the signals affects the amount of ink ejected in each drop. A printhead controller generates firing signals with reference to electronic image data to eject a pattern of individual ink drops at particular locations on the image receiving surface. The individual datum corresponding to a single drop in the electronic data is called a pixel and the locations where the drops land are sometimes called “drop locations,” “drop positions,” or “pixels.”
In order for the drop positions to correspond closely to the pixels in the electronic image data, the printheads must be registered with reference to the planar member and with reference to the other printheads in the printer. Registration of printheads is a process in which the printheads are operated to eject drops in a known pattern and then the printed image of the ejected drops is analyzed to determine the orientation of the printhead with reference to the planar member. In previously known printers, the registration process involved a human operator manually measuring a printed pattern position with reference to the edges of the planar member or by using an automated closed loop system that measured a distance of the printed pattern from a single fiducial mark on the planar member. The first registration method is susceptible to human error and the second method is subject to misidentifying the single fiducial mark as debris or other objects on the planar member that have an appearance that is similar to the single fiducial mark. Therefore, an image registration system and method that is not susceptible to human error or misidentification of the fiducial mark would be useful.